Evaluating the repeatability of corneal elevation through calculating the misalignment between Successive topography measurements during the follow up of LASIK (original) (raw)
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PloS one, 2015
To improve the reliability of corneal topographic data through the development of a method to estimate the magnitude of misalignment between successive corneal videokeratography (VK) maps and eliminate the effect of misalignment on the repeatability of topography data. Anterior and posterior topography maps were recorded twice for 124 healthy eyes of 124 participants using a Pentacam, and the repeatability of measurements was assessed by calculating the differences in elevation between each two sets of data. The repeatability of measurements was re-assessed following the determination of the magnitude of misalignment components (translational displacements: x0, y0 and z0, and rotational displacements: α, β and γ) between each two data sets and using them to modify the second data set within each pair based on an Iterative Closest Point (ICP) algorithm. The method simultaneously considered the anterior and posterior maps taken for the same eye since they were assumed to have the same...
Repeatability of corneal elevation maps in keratoconus patients using the tomography matching method
Scientific reports, 2017
To assess repeatability of corneal tomography in successive measurements by Pentacam in keratoconus (KC) and normal eyes based on the Iterative Closest Point (ICP) algorithm. The study involved 143 keratoconic and 143 matched normal eyes. ICP algorithm was used to estimate six single and combined misalignment (CM) parameters, the root mean square (RMS) of the difference in elevation data pre (PreICP-RMS) and post (PosICP-RMS) tomography matching. Corneal keratometry, expressed in the form of M, J0 and J45 (power vector analysis parameters), was used to evaluate the effect of misalignment on corneal curvature measurements. The PreICP-RMS and PosICP-RMS were statistically higher (P < 0.01) in KC than normal eyes. CM increased significantly (p = 0.00), more in KC (16.76 ± 20.88 μm) than in normal eyes (5.43 ± 4.08 μm). PreICP-RMS, PosICP-RMS and CM were correlated with keratoconus grade (p < 0.05). Corneal astigmatism J0 was different (p = 0.01) for the second tomography measurem...
Ophthalmology, 2006
To assess the repeatability and reproducibility of posterior corneal curvature (PCC) measurements made by combined scanning-slit/Placido-disc topography (Orbscan II) after LASIK. Experimental instrument validation study. We recruited 22 consecutive postmyopic LASIK patients for the repeatability study and another 50 consecutive postmyopic LASIK patients for the reproducibility study. To analyze intrasession repeatability, 1 examiner measured 22 postmyopic LASIK eyes 10 times successively in the shortest time possible. To study intersession reproducibility, the same operator obtained measurements from another 50 eyes with stable refraction in 2 consecutive visits at the same time of the day between 6 and 9 months after myopic LASIK. We explored any association between residual stromal bed thickness and measurement variability. Orbscan II scanning-slit PCC data, precision, within-subject coefficient of variation (CV(w)), limits of agreement (LoA), and intraclass correlation coefficient (ICC). For intrasession repeatability, precision was 0.067 mm (best-fit sphere [BFS]), 0.110 diopters (D; power within 5 mm), 0.158 D (power within 3 mm), and 0.46 (eccentricity). Repeatability was high for PCC BFS and power measurements within 3-mm and 5-mm zones (CV(w) ranged from 0.5%-1.2%) but poor for eccentricity data (CV(w), 31.6%). Correspondingly, ICCs ranged from 0.89 to 0.98 for PCC BFS and power, and the ICC was 0.20 for PCC eccentricity values. For intersession reproducibility, on average, no difference in PCC measurements could be found, indicating that when there is variability, it is due to random factors. The width of the 95% LoA between sessions was clinically acceptable for BFS (0.25 mm) and power (0.4 D [within 5 mm] and 0.6 D [within 3 mm]). Similarly, ICCs indicated good intersession reliability for BFS and power (0.98, 0.96, and 0.85 for BFS, power within 5 mm, and power within 3 mm, respectively) but poor reliability for eccentricity (0.59). Repeatability and reproducibility were unrelated to stromal bed thickness. Orbscan II provides reliable post-LASIK PCC data for symmetrical parameters (BFS and power), independent of the residual stromal bed thickness, but is unreliable for measurements that are radially asymmetrical (eccentricity). Orbscan II is useful for monitoring the PCC after LASIK once the early postoperative period is over.
Eye & Contact Lens: Science & Clinical Practice, 2011
To quantify the changes in the elevation topography of the front and back corneal surface after three different refractive treatments for correcting myopia with standard and custom LASIK and orthokeratology using corneal refractive therapy (CRT). METHODS: We evaluated 20 eyes undergoing orthokeratology for correction of myopia spherical equivalent (Mean±SD=-3.41±0.76D), 18 eyes undergoing custom LASIK surgery (Mean±SD=-4.14±0.89D) and 23 undergoing standard LASIK (Mean±SD=-3.61±0.67D). Values of front and back corneal surface were derived from Pentacam (Oculus, Inc. GmbH, Wetzlar, Germany) before and at least 3 months after each treatment, in the center of the cornea and 4 points to each side of the horizontal meridian at intervals of 1mm. RESULTS: Corneal elevation data before treatment were not statistically different between patients in either group (P>0.070, for back and front elevation). After treatment, both surgical procedures increased significantly the positive value of the front elevation beyond the area of 6mm. The opposite trend was found within the central 5mm of the cornea, presenting a statistically significant decrease in elevation (P<0.001). In the case of orthokeratology, the elevation suffered minor but a statistically significant reduction in the central region (P<0.001). On the back surface, the elevation did not undergo statistically significant alterations in any of the procedures and none of the items discussed (P>0.285). CONCLUSIONS: Differences in front corneal elevation changes between LASIK and orthokeratology reveal a much different mechanism for producing corneal power subtraction. The back corneal surface does not suffer significant changes after surgical and nonsurgical treatments for the correction of myopia.
Evaluation of the Orssengo-Pye IOP corrective algorithm in LASIK patients with thick corneas
Optometry - Journal of the American Optometric Association, 2005
Background: The objective of this study was to evaluate the Orssengo-Pye central corneal thickness (CCT) Goldmann applanation tonometry (GAT) corrective algorithm by observing changes in GAT and CCT before and after laser in situ keratomileusis (LASIK) surgery in patients with CCT that remains greater than 545 m postoperatively. Methods: Tonometric and pachymetric measurements were made on 14 patients (28 eyes) before and after LASIK surgery. The selected patients were required to have average or above average postoperative central corneal thickness values in both eyes (not less than 545 m). Preoperatively, all patients had CCT and GAT measurements taken. Postoperatively patients had CCT, GAT, and dynamic contour tonometric (DCT) measurements taken. Results: Preoperatively, median CCT values were 589.536 m. Median GAT values were 16.750 mmHg. Median corrected preoperative GAT values were 14.450 mmHg. After LASIK treatment, median CCT values were 559.417 m. The decrease in median CCT was 30.119 m. Median postoperative GAT values were 11.500 mmHg (decrease, 5.250 mmHg). Median corrected postoperative GAT values were 10.775 mmHg (decrease, 3.675 mmHg). Median postoperative DCT values were 17.858 mmHg. Conclusions: LASIK treatment causes a significant reduction in measured GAT intraocular pressure (IOP) values. The Orssengo-Pye formula, which attempts to correct for GAT error associated with individual variation in CCT, appears to yield misleading results in these circumstances. An unexpected 3.675-mmHg decrease in "corrected IOP" by the Orssengo-Pye method seen in this study may be attributed to some limitation or error in the formula. After adjusting for the approximate1.7-mmHg difference, which has been demonstrated between DCT and GAT, postoperative DCT values were similar to preoperative measured GAT values.
Biomédica : revista del Instituto Nacional de Salud, 2009
Anterior and posterior corneal elevations are measurements used to detect keratoconus suspects. To determine the efficacy of Orbscan II and Pentacam when assessing their elevation maps. The efficacy of the Orbscan II and Pentacam measuring the anterior and posterior corneal elevations were evaluated in a sample of 68 eyes. The concordance between the two devices and the coefficient of repeatability were measured following the parameters of the British Standard Institution by the Bland-Altman concordance analysis and the Lin concordance correlation coefficient. The coefficient of repeatability at the point of maximum anterior elevation was 68.29% with the Orbscan and 24.20% with the Pentacam. The concordance correlation coefficient was 0.64 (CI 95%: 0.48-0.76) with the Orbscan and 0.94 with the Pentacam (CI 95%: 0.91-0.96). The coefficient of repeatability at the point of maximum posterior elevation was 38.7% with the Orbscan and 68.0% with the Pentacam. The concordance correlation c...
Topography-Guided LASIK: A Prospective Study Evaluating Patient-Reported Outcomes
Clinical Ophthalmology
To evaluate patient-reported outcomes with a validated patient questionnaire following topography-guided LASIK (TG-LASIK). Methods: Patients undergoing TG-LASIK using Phorcides analytic software were prospectively enrolled to receive an adapted Patient-Reported Outcomes with LASIK Symptoms and Satisfaction (PROWL) questionnaire before and 26-weeks after treatment. The main study outcome was the change in the Global Vision Satisfaction Index from the PROWL questionnaire. Results: Forty-six patients underwent treatment and completed the modified PROWL questionnaire before and 26-weeks after TG-LASIK. The Global Vision Satisfaction Index from the modified PROWL questionnaire improved from 4.07 (3.87-4.26) to 5.00 (4.81-5.19) after the TG-LASIK treatment (p < 0.0001). The study population's binocular uncorrected distance visual acuity was 20/ 16, 20/12.5, and 20/10 or better in 100%, 87.0%, and 15.2% at 26 weeks post TG-LASIK, respectively. Conclusion: Patient satisfaction as assessed with the modified PROWL questionnaire is very high after undergoing TG-LASIK using Phorcides analytic software. Patient-reported outcomes add another dimension when assessing treatment efficacy beyond change in visual acuity and corneal architecture, and specialists may consider incorporating such assessments into the consenting process and patient education at large.
Journal of Refractive Surgery, 2013
PURPOSE: To compare the maximum posterior elevation (MPE) measurements before and after LASIK using a dual rotating Scheimpflug (DRS) imaging system (Galilei, Ziemer Ophthalmic Systems, Port, Switzerland) and a scanning slit-beam (SSB) imaging system (Orbscan IIz, Bausch & Lomb, Rochester, NY). METHODS: This retrospective study included 78 eyes from 78 patients who underwent myopic LASIK. Preoperative and postoperative data collected included anterior and posterior best-fit sphere radius and axial curvature readings, posterior central elevation (PCE), and MPE relative to a best-fit sphere using a 7.8-mm region of interest. Data were compared using paired t test analysis. RESULTS: Mean preoperative PCE (5.06 ± 2.29 μm with the DRS system and 12.78 ± 6.90 μm with the SSB system) and MPE (4.87 ± 4 μm with the DRS system and 15.44 ± 9.78 μm with the SSB system) were statistically different ( P < .001). Mean postoperative PCE (4.55 ± 2.34 μm with the DRS system and 20.59 ± 8.11 μm wit...